1. Field of the Invention
The present invention relates to a method of manufacturing a flash memory device, and more specifically, to a method of manufacturing a flash memory device in which a top layer of a gate line is comprised of a metal layer.
2. Discussion of Related Art
In DRAM/SRAM devices, stored information is lost if the supply of power is stopped. That is, in a DRAM, transistors that serve as a switch and capacitors that serve to store data constitute one cell. The DRAM is a volatile memory in which data stored in the cell is automatically lost if the supply of power is stopped. The SRAM is a volatile memory that has a transistor structure of a flip-flop type and stores data according to driving of the transistors.
On the contrary, a nonvolatile memory in which stored information is not lost although the supply of power is stopped has been developed by a developer participates in the management of a system in order to provide an operating system. The nonvolatile memory includes EPROM, EEPROM, flash EEPROM and so on. More particularly, recently, NAND type flash EEPROM has been spotlighted along with the explosive growth of mobile communication devices, MP3, digital camera, and the like.
In a manufacture process of all nonvolatile memory devices having a stack gate structure of a floating gate and a control gate, in the case where the design rule is 70 nm or less, common metal silicide (e.g., tungsten silicide) is not used as a top layer, but a metal layer (e.g., tungsten layer) has to be used due to a RC delay problem of a gate line.
In the case where the top layer of the gate line is formed of the metal layer, after the gate line is formed by means of a patterning process, an oxidization process is performed in selective oxidization mode in order to prevent abnormal oxidization of the metal layer when an oxide film is formed on sidewalls of the gate line. The selective oxidization process is a process of forming the oxide film on the sidewalls of the control gate and the floating gate while preventing abnormal oxidization from being generated in the metal layer.
If the selective oxidization process is performed, abnormal oxidization of the metal layer can be prevented, but it is implemented under a very limited condition. Thus, there are problems in that etch damages generated upon patterning of the gate line are not sufficiently compensated for, and the reliability for a tunnel oxide film is difficult to obtain.